1. Field of the Invention
The present invention relates to a wafer carrier gap washer, and more particularly, to a gap washer for washing a wafer carrier head in a CMP apparatus.
2. Description of the Prior Art
The manufacturing of integrated circuits involves applying micro-circuit structures to form a set of whole devices, of which the method is highly precise and consists of multiple steps. With the trend of integrated circuit devices towards smaller size and larger integration, more process steps are necessary in order to achieve the multilevel structure on wafers. A multilevel metallization process is used extensively in the VLSI/ULSI process, whereby a plurality of metal interconnect layers and low dielectric constant materials are used to link each of the semiconductor devices on the wafer and complete the whole stacked loop structure. However, these metal lines and semiconductor devices result in severe surface topography of integrated circuits that leads to difficulty in subsequent deposition or pattern transfer processes. Therefore, both the protruding deposition layer and uneven surface profile of the wafer need to be removed by a planarization process.
Chemical-mechanical polishing (CMP) is the most commercially applied planarization technique. CMP is similar to that of mechanical polishing in its use of the “blade” principle, of which a polishing slurry with adequate chemical additives are supplied to react with the surface of the wafer and polish the uneven surface profile of the wafer to achieve planarization. In this planarization method, the wafer is typically mounted onto a carrier head, and the exposed surface of the wafer is placed against a rotating polishing pad. The carrier head provides a controllable load, i.e., pressure, on the wafer to push it against the polishing pad. Typically, the carrier head includes a flexible membrane interposed between the wafer and the carrier head, so that the pressurized membrane forces the wafer into contact with the polishing pad. In addition, the carrier head includes a retaining ring around the wafer to hold it beneath the carrier head. A gap between the retaining ring and the flexible membrane is usually found having a mass of slurry residues after a period of polishing time. These slurry residues may bring issues such as scratches on the wafer or decrease in carrier lifetime. Therefore, there is a need for a CMP apparatus that removes slurry residues from the gap in the wafer carrier.